The development of algae-based fuels and products has been attracting interest in recent years, recognizing limitation of petroleum resources and increasing global carbon emissions. Use of microalgae as a renewable feedstock has several advantages. Microalgae are fast-growing, can be cultivated on marginal lands using low quality nutrients and water (e.g., seawater or wastewater), and exhibit high lipid productivities. The economic viability of algal biorefineries can be improved through higher-value products, such as oleochemicals, in addition to fuels. As a general rule of thumb, typical bulk price of most specialty chemicals is ˜$3/kg whereas fuels are ˜$1/kg.
Fatty acid alkanolamides (FAAAs) are lipid derivatives which are found naturally in plants and animal tissues. Industrially, they are used primarily as biosurfactants or biolubricants. Some alkanolamides have important biological roles such as anti-inflammatory activity, attenuation of pain sensation, pro-apoptotic and anorexic effects. Apart from its biological functions in living tissues, this class of lipid derivatives is used in personal care products, pharmaceuticals, detergents, rust inhibitors, ink formulations, and many other applications. FAAAs are mainly manufactured from vegetable oil with annual global demands estimated at 90,000 tons.
A number of studies have reported conversion of fatty acid triglycerides (FAG) from terrestrial biomass (i.e., vegetable oil) to alkanolamides. In general, FAAA can be synthesized by reacting alkanolamine with a fatty acyl donor, such as free fatty acids, fatty acid chlorides, fatty acid alkyl esters, and fatty acid triglycerides (FAG). Acyl chlorides have been used to deliver FAAA product with sufficient purity for biological studies, but are likely unsuitable for industrial-scale production due to cost and the corrosive nature of the reagents. Fatty acids conversion to FAAA can be accomplished using sodium methoxide catalyst but requires harsh reaction conditions due to ionic salt formation. Milder reaction conditions are conceivable with boron-based catalysts, although these catalysts have not been employed in the context of FAAA synthesis. Use of lipase is also possible for the same transformation at lower temperature and is reported to result in better product quality and color; however, enzyme cost and longevity remain a concern for the biocatalyst approach. Most commonly, direct conversion of FAG to FAAA has been studied using ethanolamine as a solvent and reactant with or without sodium methoxide catalyst. A conversion of FAG to FAAA through fatty acid methyl ester (FAME) has also been reported with analogous reaction conditions and with excellent yields for both steps. All these studies focused on converting FAGs from vegetable oils. However, traditional methods used to recover vegetable oils (FAG) from oil seeds such as mechanical “pressing” are not effective with microalgae due to microscopic size of cells and relatively tough cell walls.
In light of the fact that micro-algae is a more abundant renewable source of FAGs compared to vegetable oils, and it does not compete with food supplies, there is an urgent need for suitable and improved methods for producing biosurfactants and biolubricants from microalgae, that are simpler and cheaper, and that involve milder reaction conditions.